Carbon nanotubes (hereinafter, “CNTs”), one type of carbon-based micro structure, are carbon material that take the form of a pipe, with a diameter ranging from about 0.5 nm to about 10 nm, and a length of about 1 μm. CNTs were first discovered as a new carbon material by S. Iijima of NEC in 1991. There are two types of CNTs: single-walled nanotubes of a single-layer structure, and multi-walled tubes of a multi-layer structure.
However, due to the microstructure, CNTs are difficult to handle and process. As such, there have been attempts to fabricate CNTs of a size large enough to be handled under naked eye (see Non-Patent Publications 1 and 2, for example).
Non-Patent Publications 1 and 2 report CNTs that are longer than conventional CNTs of about 1 μm. The CNTs taught in Non-Patent Publication 1 is about 10 cm to about 20 cm long, and the CNTs taught in Non-Patent Publication 2 is about 25 cm to about 30 cm long. These CNTs can therefore be observed by naked eye.
CNTs exhibit metal-like properties or semiconductor-like properties depending on their compositions. There accordingly has been active development of products or fabrication methods that take advantage of such properties of CNTs. Potential use of CNTs as a hydrogen absorbing material, as well as applications of CNTs to fuel cell, have also been studied.
As an example of material applications of CNTs, a woven fabric or a sheet has been proposed that uses CNTs (see Patent Publication 1, for example). Patent Document 1 describes using CNTs as part of a fiber or a yarn, or a fiber or a yarn itself, and using such fiber or yarn for a woven fabric or a sheet.
(Patent Publication 1) Japanese Laid-Open Patent Publication No. 138838/1995 (published on May 30, 1995)
(Non-Patent Publication 1) H. W. Zhu, and 5 others, “Direct Synthesis of Long Single-Walled Carbon Nanotube Strands”, Science, May 3, 2002, Vol. 296, p.884-886
(Non-Patent Publication 2) Kaili Jiang, and 2 others, “Spinning continuous carbon nanotube yarns”, Nature, Oct. 24, 2002, Vol. 419, p.801
The CNTs described in Non-Patent Publication 1 are about 10 cm to 20 cm long. However, the CNTs disclosed in this publication cannot be formed easily.
The CNTs described in Non-Patent Publication 2 are fabricated from CNTs that take the form of a brush. Specifically, a plurality of CNTs are formed on a substrate by being aligned in a direction perpendicular to the substrate. The CNTs are then detached from the substrate in bundles and pulled away.
In such aggregate of CNTs, neighboring CNTs are entangled as a CNT is pulled out from the brush-like CNTs. The brush-like CNTs are therefore required to be made out of CNTs that are sufficiently long and are formed in high density.
However, in a conventional fabrication method of brush-like CNTs, the CNTs can be grown on the substrate only slowly and brush-like CNTs with long aligned CNTs cannot be obtained. Further, due to the slow growth rate of CNTs, the conventional method is disadvantageous in terms of productivity.
Another drawback of the conventional method is that the CNTs cannot be formed in high density. The brush-like CNTs therefore fail to provide enough interactions for entangling neighboring CNTs together. It is therefore difficult to obtain rope-like CNTs.
The present invention was made in view of the foregoing problems, and an object of the present invention is to provide an array of carbon-based microstructures, and an aggregate of carbon-based microstructures that are held together by strong interactions and are long enough to improve ease of handling and workability. The invention also provides various uses and a fabrication method of such array and aggregate of carbon-based microstructures.